American lawmakers are calling for full transparency in the investigation of an incident in the Iraqi town of Haditha last November, in which at least 15 Iraqi civilians were killed. The military is investigating whether U.S. Marines were responsible.

Congressman John Murtha is among the lawmakers who were briefed about the investigations so far into the incident in Haditha. He says he was told that it began when a roadside bomb killed a U.S. Marine. Murtha said he was told U.S. Marines then began firing at Iraqi civilians.

"And, then a taxi drives up," said John Murtha. "When the taxi comes up, there's four or five people in it, and they [the Marines] shoot those four or five people, [who were] unarmed. And then they [the Marines] go on a rampage throughout the houses and kill people. One woman, as I understand it in talking to the officials in the Marine Corps, was bending over her child, pleading for mercy, and they shot her in cold blood."

Speaking on the ABC television program This Week, Murtha rejected arguments that the Marines in Haditha had been responding to enemy fire.

"The reports that I have, from the highest level, [indicate] no firing at all, no interaction, no military action, at all, in this particular incident," he said. "It was an explosive device, which killed a Marine. From then on, it was purely shooting people, inside the houses and in the taxi."

The Pentagon is reportedly close to completing investigation of the Haditha incident. Officials have said, if wrongdoing is found, the perpetrators will be punished.

Murtha said he strongly believes there was an attempt to cover-up the incident. Senator John Warner, chairman of the Senate Armed Services Committee, expressed similar misgivings. But, speaking on the same ABC program, he called for calm while the U.S. military investigation is ongoing.

"This is very serious, but the military are looking at it equally serious," said John Warner. "There is this serious question, however, of what happened, and when it happened and what was the immediate reaction of senior officers in the Marine Corps when they began to gain knowledge of it."

Meanwhile, Murtha, a Vietnam War veteran and former Marine, said a transparent investigation is important to reassure the world that the United States holds its military accountable.

"They have got to put the blame where it goes and they've got to get this over with," said Congressmen Murtha.

Murtha added that, if there is misconduct within the U.S. military, making it public helps to ensure that American soldiers do not repeat it.

Besides the shooting in Haditha, the U.S. military is also looking into a separate incident in April in the Iraqi town of Hamandiyah, in which Marines are alleged to have killed an Iraqi civilian.

A Pentagon spokesman says allegations of misconduct are, in his words, "aggressively" and "thoroughly" investigated. He said the military punishes those responsible for misconduct.